The main hypothesis of the present study is that GH and sex steroid replacement can prevent or limit the decline in lean mass that occurs with aging. Specifically, the present protocol will assess the impact of hormone replacement on whole-body protein turnover, as an index of skeletal muscle protein catabolic rate. The protocol is part of an ongoing larger study of growth factors on energy expenditure, body composition and skeletal muscle mass in older persons that started in 1993. All patients for the study have been recruited through the Bayview Johns Hopkins Hospital. Each patient belongs to the age group of 65 and over and is healthy, sedentary but ambulatory.